Radical intermediates in monooxygenase reactions of Rieske dioxygenases

Sarmistha Chakrabarty, Rachel N. Austin, Dayi Deng, John Taylor Groves, John D. Lipscomb

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81 Scopus citations

Abstract

Rieske dioxygenases catalyze the cis-dihydroxylation of a wide range of aromatic compounds to initiate their biodegradation. The archetypal Rieske dioxygenase naphthalene 1,2-dioxygenase (NDOS) catalyzes dioxygenation of naphthalene to form (+)-cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene. NDOS is composed of three proteins: a reductase, a ferredoxin, and an α3β3 oxygenase (NDO). In each α subunit, NDO contains a Rieske Fe2S2 cluster and a mononuclear iron site where substrate dihydroxylation occurs. NDOS also catalyzes monooxygenase reactions for many substrates. The mechanism of the reaction is unknown for either the mono- or dioxygenase reactions but has been postulated to involve direct reaction of either a structurally characterized Fe(III)-hydroperoxy intermediate or the electronically equivalent Fe(V)-oxo-hydroxo intermediate formed by O-O bond cleavage before reaction with substrate. The reaction for the former intermediate is expected to proceed through cationic intermediates, while the latter is anticipated to initially form a radical intermediate. Here the monooxygenation reactions of the diagnostic probe molecules, norcarane and bicyclohexane, are investigated. In each case, a significant amount of the rearrangement product derived from a radical intermediate (lifetime of 11-18 ns) is observed, while little or no ring expansion product from a cationic intermediate is formed. Thus, monooxygenation of these molecules appears to proceed via the Fe(V)-oxo-hydroxo intermediate. The formation of this high-valent intermediate shows that it must also be considered as a possible participant in the dioxygenation reaction, in contrast to computational studies but in accord with previous biomimetic studies.

Original languageEnglish (US)
Pages (from-to)3514-3515
Number of pages2
JournalJournal of the American Chemical Society
Volume129
Issue number12
DOIs
StatePublished - Mar 28 2007

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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